World War I, a global conflict that reshaped the 20th century, initially saw the United States maintain a position of neutrality. However, this stance shifted dramatically in 1917, culminating in America’s entry into the war. Understanding the reasons behind this pivotal decision requires examining a series of key events and evolving political calculations that ultimately drew the U.S. into the heart of the conflict. So, why did the US join WW1? The answer is multifaceted, involving German submarine warfare, the Zimmermann Telegram, and a gradual shift in American public and political sentiment.
Germany’s aggressive naval strategy played a crucial role in altering the course of American neutrality. Initially, in response to international pressure and particularly U.S. demands, Germany had pledged to restrict its submarine warfare. The 1916 “Sussex pledge” was a direct result of American insistence after the sinking of the French vessel Sussex. Germany agreed to not attack passenger ships and to allow crews of merchant vessels to evacuate before any attack. This pledge temporarily eased tensions between the U.S. and Germany.
However, by early 1917, facing a stalemate on the Western Front and increasing domestic pressure to break the British blockade, German military and naval leaders reconsidered their strategy. They convinced Kaiser Wilhelm II that resuming unrestricted submarine warfare – targeting all ships, including those of neutral nations, in designated war zones – could cripple Great Britain and force an Allied surrender within months. German policymakers reasoned that the U.S., already supplying the Allies with munitions and financial aid, could no longer be considered truly neutral. They gambled that even if unrestricted submarine warfare provoked the United States, Germany could achieve victory before American military might could be effectively deployed in Europe. Ignoring Chancellor Theobald von Bethmann-Hollweg’s warnings about potential U.S. intervention, Germany announced the resumption of unrestricted submarine warfare on January 31, 1917. This immediately escalated tensions with the United States.
World War I Trenches in France, illustrating the brutal ground warfare that the US eventually joined in 1917.
The German decision to reinstate unrestricted submarine warfare was a direct challenge to American neutrality and freedom of the seas. President Woodrow Wilson, stunned by this announcement, severed diplomatic relations with Germany on February 3, 1917. While still hesitant to ask for a declaration of war without concrete evidence of direct German aggression against the U.S., Wilson warned Germany against attacking American ships. Despite this warning, German U-boats began targeting U.S. vessels. Throughout February and March 1917, several American ships were sunk, and American citizens lost their lives in these attacks. These actions fueled public outrage in the United States and pushed the nation closer to war.
Adding further fuel to the fire was the Zimmermann Telegram. In January 1917, British naval intelligence intercepted and decrypted a secret message from German Foreign Minister Arthur Zimmermann to the German Ambassador in Mexico. This telegram proposed a military alliance between Germany and Mexico in the event of the United States entering the war. Germany promised to help Mexico recover territories lost to the U.S. in the Mexican-American War, specifically Texas, New Mexico, and Arizona, as a reward for Mexican support.
German Chancellor Theobald von Bethmann-Hollweg, who opposed the resumption of unrestricted submarine warfare due to the risk of US intervention.
Initially, British intelligence withheld the Zimmermann Telegram from the U.S. government to protect their code-breaking operations. However, with Germany’s resumption of unrestricted submarine warfare and the increasing likelihood of U.S. involvement, the British decided to release the telegram to sway American public opinion decisively towards war. The British delivered the intercepted telegram to President Wilson on February 24, 1917, and it was widely publicized in the American press the following week.
The Zimmermann Telegram, a secret communication intercepted by British intelligence, which proposed a German-Mexican alliance against the US.
The Zimmermann Telegram ignited public outrage in the United States. The idea of a German-backed Mexican invasion of American soil was deeply alarming and perceived as a direct and hostile threat to U.S. security. Combined with the ongoing submarine attacks on American shipping, the Zimmermann Telegram proved to be a decisive factor in shifting public opinion in favor of war.
Despite the mounting pressure, President Wilson initially hesitated. He convened his Cabinet on March 20, 1917, to discuss the path forward. Wilson, who had strived to maintain peace and had previously avoided war even after the sinking of the Lusitania and Arabic in 1915, now faced a dramatically changed situation. The continuous submarine attacks, coupled with the provocative Zimmermann Telegram, convinced Wilson that Germany was not interested in a peaceful resolution and posed a direct threat to the United States. Furthermore, international law at the time suggested that arming merchant ships with naval personnel, which Wilson had authorized, could be construed as an act of war.
Ultimately, the combination of Germany’s unrestricted submarine warfare, which directly threatened American lives and commerce, and the Zimmermann Telegram, which revealed a hostile German intent towards U.S. territory, proved to be the tipping point. These factors swayed both public opinion and President Wilson’s administration, leading to the conclusion that war was unavoidable. On April 2, 1917, President Wilson addressed a joint session of Congress, requesting a declaration of war against Germany. Congress granted his request, and on April 6, 1917, the United States officially entered World War I, marking a turning point in both American history and the global conflict. The reasons for US entry into WW1 were thus complex, but fundamentally rooted in the defense of national interests and the response to direct German provocations.
